A wireless base station may be divided into two parts in view of function: a radio equipment control (REC) part which can also be called a base band (BB) part and a radio equipment (RE) part which can also be called a radio frequency module (RFM) part. The above base band part and the radio frequency module part may also be called a BBU and an RRU respectively, which essentially refer to the two parts of the base band digital part and the radio frequency part. The above base band part and the radio frequency module part are represented as REC/BB and RE/RFM hereinafter, respectively.
One REC/BB may correspond to a plurality of RE/RFMs. Regarding the physical position, the REC/BB and the RE/RFM may be set together, and may also be set separately. A standard or nonstandard interface mode is used between the REC/BB and the RE/RFM. The common public radio interface (CPRI) and the open base station architecture initiative (OBSAI) interface are typical standard interfaces. The base band radio frequency interface is generally called as BR (base band and radio frequency) interface hereinafter, which may be the CPRI and the OBSAI, and may also be a self-defined protocol interface.
The wireless base station often requires synchronization in the whole network, i.e., the REC/BB synchronizes with all of the RE/RFMs, while in the prior art, the method for solving the synchronization in the whole network is to set a time distributor on the REC/BB side, and then the clock is distributed to all of the RE/RFMs through the time distributor on the REC/BB side, as shown in FIG. 1.
FIG. 2 is a diagram of the network architecture of the conventional CPRI. As can be seen from FIG. 2, the clock source is located at the REC, the clock is transmitted on the CPRI interface through the message fields such as Z.0.0 (start of hyper-frame, K28.5), Z.64.0 (hyper-frame number), and Z.128.0/Z.192.0 (NodeB frame number), and the RE receives these messages from the CPRI interface and keeps the synchronization in the whole network using these messages.
FIG. 3 is a diagram of the network architecture of the conventional OBSAI. As can be seen from FIG. 3, in the BB module there is a control & clock module (called Con. & Clock for short in the figure) which is responsible for generating a reference clock, and then the synchronous signal is transmitted to the RFM through an RP3 interface by using the fields or the messages such as K28.7, frame clock burst, system frame time (SFN), and time stamp. Then, the RFM keeps the synchronization with other network elements according to the synchronization information obtained.
The above technical scheme that the clock source is located at the REC/BB and distributed to the RE/RFM by the base band radio frequency interface has the following problems: part of the time receivers (for example GPS) depends on antennas, while the position at which the REC/BB is set is often not suitable for arranging an antenna. Therefore, the antenna shall be connected to the REC/BB from a position which is suitable for arranging the antenna, which brings out complexity in the engineering aspect and even can lead the network construction to be infeasible.
An improved technology is to set the time receiver (for example GPS) at the outside of the base band, and then the clock synchronous signals are transmitted to the base band through a dedicated cable. The defect of this improved technology lies in that a cable for transmitting the clock/synchronous signals still needs to be added, which indeed can bring inconvenience for the engineering just the same as by adding the receiving antenna, meanwhile, if this technology is used, circuits such as lightening-proof need to be added at the base band part correspondingly, and the reliability of the long distance transmission is also a problem.
It can be seen that all the above-mentioned technologies have the problems such as difficulty in engineering installation, high cost, and low reliability.